Redirecting Input and Output

Output

2 types of outputs
- Standard output is for normal program messages
- Standard error contains error messages
  - represented by 2 at the CLI
separates errors from standard outputs so they don’t causes issues for programs that take as input outputs from other programs

Redirection Operator	Effect
`>`	Creates a new file containing the standard output, or overwrites if exists.
`>>`	Appends standard output to the existing file, or creates if not existent.
`2>`	Creates a new file containing error messages (standard error), or overwrites if exists.
`2>>`	Appends standard error to the existing file, or creates if doesn’t exist.
`&>`	Creates a new file containing both standard output and standard error, or overwrites if exists.
`<`	Sends the contents of the specified file to be used as standard input.
`<<`	Accepts text on the following lines as standard input.
`<>`	Causes the specified file to be used for both standard input and standard output.

can redirect standard errors to /dev/null to discard them
- is a device that serves as a trash can

A pipeline |, or pipe, redirects standard output from one program as standard input to a second program.

The xargs command’s purpose in a pipeline is to build a command from its standard input.

syntax: xargs [OPTIONS] [COMMAND [INITITAL-ARGUMENTs]]
- COMMAND is the command you want to execute
- [OPTIONS] are xargs options; not passed to COMMAND
when you run it, it runs command once for every word passed to it on standard input, adding that word to the argument list for COMMAND
to pass multiple options to the command, protect them in enclosing quotes

Backticks `` take text placed within them and treat it as a separate command whose results are substituted on the command line.

$() is a command substitution format that executes the command placed within it first.